Papers by Keyword: XANES

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Authors: Li Zhu Liu, Xuan Pan, Xu Xia, Yu Hang Zhou, Zhen Yuan Nie, Jin Lan Xia
Abstract: The differences of superficial (about 10 nm) extracellular polymeric substances (EPS) composition of thermoacidophilic archaea Acidianus manzaensis YN-25 acclimated with different energy substrates (FeS2, CuFeS2, S0, FeSO4) were analyzed in situ for the first time by synchrotron radiation (SR) based carbon K-edge X-ray absorption near edge structure (XANES) spectroscopy. The results showed that there are clear associations between the energy substrates and the changes in organic composition in terms of typical function groups (-C=O, -C-O and -C-N). The archaea acclimated with chalcopyrite and pyrite contain higher proportion of proteins but less polysaccharides compared to cells acclimated with S0.The archaea acclimated with FeSO4 contains the highest proportion of protein which is positively associated with the iron oxidation process, while archaea acclimated with S0 contains more lipids and polysaccharides, which may be favorable to the hydrophobic S0 adsorption and utilization processes.
Authors: C.G.H. Walker, S.A. Morton, J.M. Charnock, E.J. MacLean, Norman M.D. Brown
Authors: Yi Yang, Wei Hua Liu, Chun Wang, Miao Chen, Rahul Ram, Suresh K. Bhargava
Abstract: In the present study, we investigated the bioleaching of arsenopyrite with or without pyrite by moderate thermophiles. In both chemical leaching and bioleaching, the addition of pyrite decreased the leaching rate of arsenopyrite. The arsenic speciation and minerology changes in the residues were analysed by X-ray Absorption Near Edge Structure (XANES) Spectroscopy, X-ray Photoelectron Spectroscopy (XPS) and powder X-ray Diffraction (XRD). The XANES analysis showed no detectable arsenopyrite in the final residues from the experiments without pyrite. However, there was still 21.7% of arsenic species presented as arsenopyrite after bioleaching, when the initial arsenopyrite/pyrite ratio was 1:5. The XPS analysis revealed there was only As(V) on the surface of most of the residues, except on one chemically leached sample where As(III) was found.
Authors: G. Cordeiro Silva, Regina Pinto de Carvalho, M. Sylvia S. Dantas, Virgínia S.T. Ciminelli
Abstract: The biosorption of arsenic species by dried lettuce leaves (L.sativa) was investigated. Arsenic sorption, that is not effective on in natura biomass, was enhanced when the biomass was previously loaded with Fe(III). Analysis of X-ray Absorption Near-Edge Spectroscopy (XANES) spectra showed that iron was incorporated as Fe(III) and arsenic as As(V), regardless the contact with the lowest or highest valence species of these elements. The features of Extended X-ray Absorption Fine-Structure Spectroscopy (EXAFS) spectra suggest that the nearest neighboring atoms of iron ions are the same in all the samples, even in the As-Fe loaded ones. These results indicate the arsenic oxyanions as the sorbed species on the iron-loaded biomass.
Authors: Aline Léon, Oliver Kircher, Jörg Rothe, Maximilian Fichtner
Authors: Hsin Liang Huang, H. Paul Wang, Y.L. Wei, Tung Li Hsiung
Abstract: X-ray absorption near edge structural (XANES) and X-ray absorption fine structural (EXAFS) spectroscopies have been used to study chemical structure of nanosize copper extracted in the channels of MCM-41. The component-fitted XANES spectra show that about 95% of copper are adsorbed on the surfaces of MCM-41 at 298 K. A small amount of nanosize CuO in MCM-41 is also found. The adsorbed copper (Cu(II)(ads)) in the channels of MCM-41 may be oxidized and form nanosize CuO as calcined at 573 and 923 K. By EXAFS, it is observed that the nanosize CuO in MCM-41 possesses a Cu-O bond distance of 1.97 Å with a coordination number (CN) of 2.6, indicating the existence of linear type Cu3O4 cluster. Interestingly, calcinations of the nanosize CuO in MCM-41 at 923 K has led to a formation nanowire-type CuO (in the channels of MCM-41) with a length of 50-100 nm and width of about 5-9 nm.
Authors: Hong Chang Liu, Jin Lan Xia, Zhen Yuan Nie, Hong Rui Zhu, Yi Dong Zhao, Chen Yan Ma, Lei Zheng, Cai Hao Hong
Abstract: Differential utilization of isomers pyrite and marcasite by Acidianus manzaensis were comparatively studied, besides the iron and sulfur speciation transformation of the minerals was also investigated based on synchrotron radiation X-ray absorption near edge structure (XANES) spectroscopy. The results showed that the biooxidation of pyrite was faster than marcasite. The bioleached surface of both pyrite and marcasite are serious corroded, and the Fe (III)-containing species as well as jarosite were gradually produced, and more elemental sulfur species were formed on the marcasite surface than that for pyrite. It demonstrates the mineral structure does affect the biooxidation of pyrite and marcasite, and the more precipitated elemental sulfur might be one of the reasons leading to lower oxidation rate of marcasite by A. manzaensis.
Authors: Tomoko Yoshida, Shunsuke Muto, Jun Wakabayashi
Abstract: Energetic nitrogen ion was injected into a TiO2 photocatalyst in order to investigate the optimal local concentration of doped nitrogen for visible-light response. N+-implanted TiO2 samples promoted the photocatalytic activity under visible-light irradiation. N K-edge XANES of the highest activity sample indicated that N replaces the O sites near the surface, whereas in the samples of higher N+ fluence, N−O and/or N−N species formed. Depth-resolved N K-edge ELNES revealed the two types of N, depending on the concentration, and we found the local N concentration effective for visible-light response was less than ∼1 at%. Further, the spatial distributions of the different chemical states of N by energy-filtering TEM (FETEM) supported these findings.
Authors: Jeevan Jadhav, Somnath Biswas, A.K. Yadav, S.N. Jha, D. Bhattacharyya, N.K. Sahoo
Abstract: In this paper, we report the experimental observations of the effects of Ni concentration on the structural and magnetic properties of NixZn1-xFe2O4 (x=0.2-0.8) ferrite nanoparticles synthesized by a chemical method via a polymer precursor. The synthesis process involves a reaction of aqueous solutions of metal salts (Fe3+, Zn2+ and Ni2+) with an aqueous poly-vinyl alcohol (PVA)-sucrose solution at 65-70oC. Controlled growth of the ferrite nanoparticles was achieved by encapsulation of the nucleating sites in the PVA-sucrose polymer micelles. Structural properties of the derived samples were analyzed with X-ray diffraction (XRD) and X-ray absorption near edge spectroscopy (XANES) studies. The magnetic properties of the NixZn1-xFe2O4 (x=0.2-0.8) nanoparticles were evaluated at room temperature with a vibrating sample magnetometer (VSM). XRD analysis confirmed the formation of single phase cubic spinel ferrite structure. The local structural analysis of the Ni-Zn ferrite crystal system performed with XANES studies at Fe K-edge revealed the migration of Fe3+ ions from the octahedral sites to tetrahedral sites with the increase in Ni2+concentration in the ferrite structure.It was observed that the magnetization increases with the increase in Ni concentration till the maximum saturation magnetization was observed in the composition Ni0.5Zn0.5Fe2O4. Further increase in Ni concentration reduces the magnetization. The obtained results were analyzed in correlation with the cationic distributions at the lattice sites in these ferrite nanoparticles.
Authors: H.S. Isaacs, D.N. Kalonousky, S. Virtanen, M.P. Ryan
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